This invention relates to a process for producing false-twist textured yarn, and is more particularly concerned with applying false-twist to yarn with hollow friction tubes.
False-twist texturing processes have used a variety of devices for applying false twist. The hollow friction tube, fitted with a toroidal bushing of high friction material on each end, is a particularly preferred type of false twister. One advantage of such a twister is its high rate of twist generation, due primarily to the fact that many turns of twist are inserted into the traveling yarn for each rotation of the tube. Such tubes are, moreover, relatively easily and inexpensively fabricated. Stringup of yarn through their relatively large axial openings is simple, and they are small enough to be readily positioned on existing yarnhandling equipment such as uptwisters, downtwisters, draw twisters, and the like. When increased torque is desired for obtaining a given degree of twisting, two (or more) hollow friction tubes may be used in series, as is known.
Hollow friction-twist tubes have been fitted at each end with identical toroidal bushings of deformable elastomeric material with high yarn-to-bushing friction and good resistance to wear. Generally the materials used for bushings comprise either hard rubber or synthetic elastomers (e.g., polyurethanes).
As higher and higher processing speeds are attempted, eventually a point is reached at which yarn instability occurs with the result that twist insertion becomes erratic and spaced twisted sections of yarn slip through the friction tube. The onset of instability can be moved to a greater yarn speed by increasing the yarn tension so as to keep the yarn more firmly in contact with the friction surfaces. This approach, however, quickly leads to tensile failure of the yarn being processed. Moreover, increase of yarn tension during false twisting undesirably increases the amount of shrinkage of the packaged yarn.
Chimura et al. disclose in German Patent No. 2,245,468, dated Apr. 5, 1973, that it is possible to produce a uniform and strong crimp even at a yarn running velocity of above 300 meters per minute, and to produce thereby a uniform crimped and bulked yarn, when the value of 1000 V/S is between 300-D and 500-D, and the ratio of T.sub.2 /T.sub.1 is below 2, where:
V is the yarn running velocity in m/min. on the frictional surface producing the twist, PA1 S is the peripheral velocity in m/min. in the middle of the frictional surface part cooperating with the yarn, PA1 D is the denier count of the yarn to be crimped, PA1 T.sub.1 is the yarn tension in grams at the inlet side of the twist producing tube, and PA1 T.sub.2 is the yarn tension in grams at the exit side of the twist producing tube.
The patent teaches that the process can be used with all thermoplastic synthetic yarns for which false twisting is possible. The process is illustrated with conventional polyester an polyamide feed yarns; the illustrations include ones where the operations of drawing and false-twist texturing are combined. The false-twist texturing equipment disclosed appears to be conventional except for the use of a cooling roll between the heater and the false-twist tube. Most of the illustrations use a tube fitted at each end with a toroidal bushing of a wear and tear resistant material with a high frictional value, polyurethane being the only material mentioned, and having an inner diameter of 35 mm. at the middle part of the surface cooperating with the yarn.
The present invention is an improvement over processes such as that of the above patent.